This relates generally to imaging devices, and more particularly, to imaging devices having compact image sensor pixels with high dynamic range functionalities.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an image sensor includes an array of image pixels arranged in pixel rows and pixel columns. Circuitry may be coupled to each pixel column for reading out image signals from the image pixels.
Typical image pixels contain a photodiode for generating charge in response to incident light. Image pixels may also include a charge storage region for storing charge that is generated in the photodiode. Image sensors can operate using a global shutter or a rolling shutter scheme. In a global shutter, every pixel in the image sensor may simultaneously capture an image, whereas in a rolling shutter each row of pixels may sequentially capture an image.
Image sensors may be equipped with multi-exposure high dynamic range (HDR) functionality, where multiple images are captured with an image sensor at different exposure times. The images are later combined into a high dynamic range image. A HDR image sensor can operate using a rolling shutter operation or a global shutter operation by adding additional sample and hold (S/H) circuitry. However, the additional sample and hold circuitry may take up valuable pixel area, decreasing the amount of active area available for the pixel photodiode. Additionally, in standard HDR image sensor pixels, bright scenes can cause unwanted saturation of the photodiode leading to over saturated image signals.
It would therefore be desirable to be able to provide imaging devices with improved image sensor pixels.